Microscopic phase-field simulation coupled with elastic strain energy for precipitation process of Ni-Cr-Al alloys with low Al content

The precipitation process of Ni-Cr-Al alloy with low Al content was studied at atomic scale based on the microscopic phase-field kinetic model coupled with elastic strain energy. The aim is to investigate the effect of elastic strain energy on precipitation mechanism and morphological evolution of the alloy. The simulation results show that in the early stage of precipitation, Do₂₂ phase and L1₂ phase present irregular shape, and they randomly distribute in the matrix. With the progress of aging. L1₂ phase and D0₂₂ phase change into the quadrate shape and their orientations become more obvious. In the later stage, L1₂ phase and D0₂₂ phase present quadrate shape with round corner and align along the [100] and [010] directions, and highly preferential selected microstructure is formed. The mechanism of early precipitation of L1₂phase in Ni-17%Cr-7.5%Al (mole fraction) alloy is the mixed style of non-classical nucleation growth and spinodal decomposition and the D0₂₂ phase is the spinodal decomposition. The mechanisms of early precipitation of L1₂ phase and D0₂₂ phase in Ni-12.5%Cr-7.5% Al alloy are both the non-classical nucleation and growth. The coarsening process follows the rule of preferential selected coarsening.